Pedicle screw with detachable polyaxial head

ABSTRACT

A pedicle screw device for fixating at least two adjacent vertebral bodies is presented. The device consists of a bone screw which is implanted into the pedicle of a vertebral body. A second bone screw is implanted into the pedicle of a second vertebral body. A polyaxial head is then inserted over each bone screw. The polyaxial heads can then be slid into a retaining position on the bone screw, allowing them to rotate about the spherical portion of the bone screw. The polyaxial heads are then attached to one another with a rod. Finally, a locking screw is inserted into the polyaxial heads to force the rod against the bone screw as well as the polyaxial head, locking them in place. The rod also serves to prevent the polyaxial head from disconnecting from the bone screw.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation and claims the benefit of U.S. patentapplication Ser. No. 17/219,828, filed on Mar. 31, 2021, and entitled“Pedicle Screw with Detachable Polyaxial Head”, the entire disclosure ofwhich is incorporated herein by reference.

FIELD OF INVENTION

The present invention relates to a pedicle screw implant assembly, andmore particularly, a pedicle screw with an offset and removablepolyaxial head.

BACKGROUND OF INVENTION

While certain existing pedicle screws include detachable, or modular,polyaxial heads, those pedicle screws with detachable heads generallyrely on the detachable head being axial to the bone screw body. Inparticular, existing detachable heads are generally attached either bythreading the polyaxial head onto the pedicle screw, or by means of anexpandable portion, either in the polyaxial head itself, or by means ofa collet.

There are significant drawbacks to both of these methods. First,threading a polyaxial head over a screw can result in merely driving thebone screw further into pedicle, which can have seriously dangerousconsequences, such as driving the screw through the anterior wall of thevertebral body. Also, threading a polyaxial head over a screw could alsolead to seating the bone screw too deep into the pedicle, therebypreventing the polyaxial head from properly seating onto the bone screw.Furthermore, threading a polyaxial head over a screw can cause thethreads on the bone screw head to deform during tightening, therebypreventing proper rigid fixation.

Similarly, there are disadvantages in using a collet as an attachmentmechanism to secure a polyaxial head to a bone screw. A collet is ableto connect over a bone screw, because the collet elastically deformsopen during attachment of the polyaxial head to the bone screw head,thereby relying on the elasticity of the metal to return to its originalshape and size to secure to the bone screw head. While this can createan attachment, it also creates a weak point, as the collet can reopenunexpectedly. Typically, this happens when the collet and bone screwhead are not properly seated together or can happen when soft tissueimpedes proper seating. Moreover, collets are known to become unseatedfrom the bone screw head even after the entire construct is locked inplace, including after surgery, when the forces of the spine act to pullthe rod and polyaxial head away from the bone screw, resulting in afailed fusion and the need for a second surgery.

Therefore, there is a need in the art for a pedicle screw system with apolyaxial head that can be attached to the screw head by a means otherthan by threading the head onto the bone screw or through attachment viaa collet. These and other features and advantages of the presentinvention will be explained and will become obvious to one skilled inthe art through the summary of the invention that follows.

SUMMARY OF THE INVENTION

Accordingly, it is an aspect of the present invention to provide apedicle screw system configured with a polyaxial head that attachesunder the bottom of the head of the bone screw and is configured toreceive the head of the bone screw in a cavity formed in the polyaxialhead. The poly axial head is further configured with a channel thatreceives a fusion rod and a threaded portion that receives lockingscrew, with the fusion rod channel being formed continuously with thecavity that receives the head of the bone screw. Collectively, thefusion rod and locking screw operate to secure the head of the bonescrew with the cavity.

According to an embodiment of the present invention, a pedicle implantassembly comprising a polyaxial head comprising a vertical screw headchannel formed within a first lateral side of the polyaxial head, aspherical screw head aperture formed within a second lateral side of thepolyaxial head, and a horizontal screw head channel connecting betweenthe vertical screw head channel and the spherical screw head aperture.

According to an embodiment of the present invention, the pedicle implantassembly further comprises a bone screw formed with a spherical head, aneck portion, and a threaded portion.

According to an embodiment of the present invention, the neck of thebone screw is narrower than the spherical head and threaded portion ofthe bone screw.

According to an embodiment of the present invention, the pedicle implantassembly further comprises a pair of retaining tabs, wherein the pair ofretaining tabs are positioned between the horizontal screw head channeland the spherical screw head aperture.

According to an embodiment of the present invention, the pair ofretaining tabs are configured to flex outward when a head portion of abone screw is moved between the horizontal screw head channel and thespherical screw head aperture.

According to an embodiment of the present invention, the pedicle implantassembly further comprises a screw neck aperture formed in a bottom faceof the polyaxial head.

According to an embodiment of the present invention, the screw neckaperture terminates at, and is formed continuously with, a bone screwopening formed at the first lateral side of the polyaxial head.

According to an embodiment of the present invention, the pedicle implantassembly further comprises a rod slot formed within the first lateralside of the polyaxial head.

According to an embodiment of the present invention, the rod slot isopen at a top side of the polyaxial head and is formed with a threadedportion at a top edge of the rod slot.

According to an embodiment of the present invention, the rod slot andthe vertical screw head channel share a center axis.

According to an embodiment of the present invention, a pedicle implantassembly comprising a polyaxial head comprising a vertical screw headchannel formed within a first lateral side of the polyaxial head, aspherical screw head aperture formed within a second lateral side of thepolyaxial head, a horizontal screw head channel connecting between thevertical screw head channel and the spherical screw head aperture, and apair of retaining tabs configured to retain a bone screw within thespherical screw head, wherein the pair of retaining tabs are aligned onopposite walls of the polyaxial head and between the spherical screwhead aperture and the horizontal screw head channel.

According to an embodiment of the present invention, the bone screw isformed with a spherical head, a neck portion, and a threaded portion andthe neck portion of the bone screw is narrower than the spherical headand threaded portion of the bone screw.

According to an embodiment of the present invention, the pair ofretaining tabs are configured to flex outward from the horizontal screwhead channel as the spherical head of the bone screw is moved from thehorizontal screw head channel into the spherical screw head aperture.

According to an embodiment of the present invention, the pedicle implantassembly further comprises a screw neck aperture formed in a bottom faceof the polyaxial head, wherein the screw neck aperture is wider than theneck portion of the bone screw and narrower than the spherical head ofthe bone screw.

According to an embodiment of the present invention, the vertical screwhead channel intersects with the screw neck aperture at the firstlateral side of the polyaxial head and is configured to accommodate thespherical head of the bone screw.

According to an embodiment of the present invention, the pedicle implantassembly further comprises a rod slot formed within the first lateralside of the polyaxial head, wherein a lateral sidewall of the rod slotis formed continuously with a lateral sidewall of the vertical screwhead channel and a medial sidewall of the rod slot terminates at thescrew head aperture.

According to an embodiment of the present invention, a pedicle implantassembly comprising a pedicle implant assembly comprising a bone screwformed with a spherical head, a neck portion, and a threaded portion,wherein the neck of the bone screw is narrower than the spherical headand threaded portion of the bone screw; and a polyaxial head acomprising a screw neck aperture formed in a bottom face of thepolyaxial head and a vertical channel opening formed in the bottom faceof the polyaxial head, wherein the screw neck aperture is narrower thanthe spherical head of the bone screw and the vertical channel opening iswider than the spherical head of the bone screw.

According to an embodiment of the present invention, the pedicle implantassembly further comprises a spherical screw head aperture formed in thepolyaxial head above an end of the screw neck aperture that is oppositethe vertical channel opening and a horizontal screw head channel formedcontinuously with, and extending away from, the spherical screw headaperture toward the vertical channel opening.

According to an embodiment of the present invention, the pedicle implantassembly further comprises a pair of retaining tabs, wherein the pair ofretaining tabs are positioned between the horizontal screw head channeland the spherical screw head aperture.

According to an embodiment of the present invention, the pedicle implantassembly further comprises a vertical screw head channel extending froma top face of the polyaxial head and terminating at the vertical channelopening.

The foregoing summary of the present invention with the preferredembodiments should not be construed to limit the scope of the invention.It should be understood and obvious to one skilled in the art that theembodiments of the invention thus described may be further modifiedwithout departing from the spirit and scope of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of two adjacent of vertebrae with a pediclescrews implanted in each of the vertebrae.

FIG. 2 is a perspective view of a first preferred embodiment of apolyaxial head being placed over a pedicle screw implanted in each oftwo adjacent vertebrae.

FIG. 3 is a perspective view of a first preferred embodiment of apolyaxial head attached in an unsecured position on a pedicle screwimplanted in each of two adjacent vertebrae.

FIG. 4 is a perspective view of a first preferred embodiment of apolyaxial head attached in fixed position on a pedicle screw implantedin each of two adjacent vertebrae.

FIG. 5 is a perspective view of a rod being inserted between a firstembodiment of a polyaxial head on each of two adjacent vertebrae.

FIG. 6 is a perspective view of a locking screw fastening to a polyaxialhead on each of two adjacent vertebrae in order to secure a rod withinthe polyaxial heads.

FIG. 7 is a perspective view of a first preferred embodiment of apedicle screw and polyaxial head assembly.

FIG. 8 is a side view of a first preferred embodiment of a pedicle screwand polyaxial head assembly.

FIG. 9 is a sectioned side view of a first preferred embodiment pediclescrew and polyaxial head assembly with the pedicle screw unsectioned.

FIG. 10 is an exploded perspective view of a first preferred embodimentof a pedicle screw and polyaxial head assembly.

FIG. 11 is a perspective view of a first preferred embodiment of apedicle screw and polyaxial head assembly with the polyaxial headmounted on the pedicle screw in an unsecured position.

FIG. 12 a perspective section view of a first preferred embodiment of apedicle screw and polyaxial head assembly with the polyaxial headmounted on the pedicle screw in an unsecured position.

FIG. 13 is a perspective section view of a first preferred embodiment ofa pedicle screw and polyaxial head assembly with the polyaxial headmounted on the pedicle screw in a fixed position.

FIG. 14 is a lower perspective view of a first preferred embodiment of apedicle screw and polyaxial head assembly with the polyaxial headmounted on bone screw in an unsecured position.

FIG. 15 is a lower perspective view of a first preferred embodiment of apedicle screw and polyaxial head assembly with the polyaxial headmounted on bone screw in a fixed position.

FIG. 16 is a perspective view of a first preferred embodiment of apedicle screw and polyaxial head assembly depicting the insertion of arod into the polyaxial head.

FIG. 17 is a perspective view of a first preferred embodiment of apedicle screw and polyaxial head assembly depicting the fastening of alocking screw onto polyaxial head.

FIG. 18 is a side view of a second preferred embodiment of a pediclescrew and polyaxial head assembly.

FIG. 19 a perspective section view of a second preferred embodiment of apedicle screw and polyaxial head assembly with the polyaxial headmounted on the pedicle screw in an unsecured position.

FIG. 20 is a sectioned side view of a second preferred embodimentpedicle screw and polyaxial head assembly with the pedicle screwunsectioned.

FIG. 21 is a perspective section view of a first preferred embodiment ofa pedicle screw and polyaxial head assembly with the polyaxial headmounted on the pedicle screw in a fixed position.

DETAILED DESCRIPTION

In the Summary above and in this Detailed Description, and the claimsbelow, and in the accompanying drawings, reference is made to particularfeatures of various embodiments of the invention. It is to be understoodthat the disclosure of embodiments of the invention in thisspecification includes all possible combinations of such particularfeatures. For example, where a particular feature is disclosed in thecontext of a particular aspect or embodiment of the invention, or aparticular claim, that feature can also be used—to the extentpossible—in combination with and/or in the context of other particularaspects and embodiments of the invention, and in the inventiongenerally. It should be noted that the features illustrated in thedrawings are not necessarily drawn to scale and descriptions ofwell-known components and techniques may be omitted so as to notunnecessarily obscure the embodiments.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthis detailed description. The invention is capable of myriadmodifications in various obvious aspects, all without departing from thespirit and scope of the present invention. Accordingly, the drawings anddescriptions are to be regarded as illustrative in nature and notrestrictive.

In accordance with embodiments of the present invention, a pedicle screwimplant assembly disclosed herein is configured to fix two adjacentvertebrae. In a preferred embodiment, as depicted by at least FIGS. 1-7, the implant assembly 10 comprises at least two bone screws 20, eachwith a detachable, offset polyaxial head 30, with a bone screw 20 beingimplanted into each of two adjacent vertebrae V1, V2. The implantassembly 10, further comprises an elongated cylindrical rod 40 thatconnects the polyaxial heads 30 of the bones screws 20 together.Finally, locking screws 50 secure the rod 40 to the polyaxial heads 30and thereby fixing the two adjacent vertebrae V1, V2 together.

In a preferred embodiment, as shown by at least FIG. 10 and FIG. 13 ,the bone screw 20 component is comprised of an elongated bone threadportion 21 that is configured to thread into and anchor to the vertebralbody. At the proximal end of the bone thread portion 21, is cylindricalneck portion 22 that is relatively narrower than the other portions ofthe bone screw 20. Sitting atop the neck portion 22 is a spherical head23, the diameter of which is larger than the neck 22. A drive feature 24configured to receive a screw driver is formed inside of the sphericalhead 23.

In a preferred embodiment, as best shown by FIGS. 1-3 , at least onebone screw 20 is implanted into the pedicle of at least two adjacentvertebrae V1, V2. The bone screws 20 are inserted into the vertebrae V1,V2, so as to leave the neck 22 and spherical head 23 portions of thebone screws 20 exposed above the bone of the pedicle. A polyaxial head30 component is then placed over the spherical head 23 of each bonescrew 20.

In a preferred embodiment, as shown by at least FIGS. 10-13 , thepolyaxial head 30 is formed with a vertical screw head channel 31running along the proximal-distal axis. In the preferred embodiment, thevertical screw head channel 31 is nominally the same diameter as thespherical head 23 of the bone screw 20. The vertical screw head channel31 extends through the bottom face of the polyaxial head 30 creating anopening that is the full diameter of the vertical screw head channel 31.The opening of the vertical screw head channel 31 formed in the bottomface of the polyaxial head 30 may be continuous with, and define theterminus of the first end of, the screw neck aperture 34. To attach thepolyaxial head 30 to the bone screw 20, the vertical screw head channel31 of the polyaxial head 30 is slid over the spherical head 23 of bonescrew 20.

When the polyaxial head 30 is in place over the bone screw 20 with thespherical head 23 within the vertical screw head channel 31, thepolyaxial head 30 is in the unrestrained position or unsecured position,wherein there is no mechanism securely fastening the polyaxial head 30together with the bone screw 20. The polyaxial head 30 is configured toslide over the spherical head 23 of the bone screw 20 so that thespherical head 23 slides within the horizontal screw head channel 32polyaxial head 30. In a preferred embodiment, as shown by at least FIG.12 and FIG. 13 , the horizontal screw head channel 32 is nominally thediameter of spherical head 23 of the bone screw 20 and runsperpendicular to the vertical screw head channel 31. In the preferredembodiment, the center point of the horizontal screw head channel 32 isabove the bottom face of the polyaxial head 30, such that the horizontalscrew head channel 32 aligns with the screw neck aperture 34 formed inthe bottom face of the polyaxial head 30.

In a preferred embodiment, as shown by at least FIG. 14 and FIG. 15 ,the screw neck aperture 34 has a width that is less than the width ofspherical head 23 of the bone screw 20, but greater than the width ofthe neck 22 of the bone screw 20. This enables the polyaxial head 30 toslide horizontally over the bone screw 20, with the neck 22 passingthrough the screw neck aperture 34, while the spherical head 23 passesthrough the horizontal screw head channel 32. With the spherical head 23being wider than the screw neck aperture 34, the polyaxial head 30 isprevented from being lifted off of the bone screw 20. As the polyaxialhead 30 slides horizontally over the spherical head 23 of the bone screw20 toward the spherical screw head aperture 33, the polyaxial head 30remains in the unrestrained position or unsecured position. In thepreferred embodiment, a first end of the screw neck aperture 34terminates at the opening of the vertical screw head channel 31 formedin the bottom face of the polyaxial head 30 and a second end of thescrew neck aperture 34 terminates below the spherical screw headaperture 33. In some embodiments, the opening of the vertical screw headchannel 31 formed in the bottom face of the polyaxial head 30 may becontinuous with the screw neck aperture 34, with the opening of thevertical screw head channel 31 being wider than the screw neck aperture34 and thereby marking the boundary between the opening of the verticalscrew head channel 31 and the screw neck aperture 34.

In a preferred embodiment, as shown by least FIG. 12 and FIG. 13 , thehorizontal screw head channel 32 connects the vertical screw headchannel 31 to the spherical screw head aperture 33 of the polyaxial head30. In the preferred embodiment, the spherical screw head aperture 33has the same center point and diameter as the horizontal screw headchannel 32 and likewise aligns with the screw neck aperture 34 formed inthe bottom face of the polyaxial head 30, such that the spherical screwhead aperture 33 is above the terminal end of the screw neck aperture 34that is opposite the vertical screw head channel 31 screw neck.Therefore, when the spherical head 23 of the bone screw is within thespherical screw head aperture 33 of the polyaxial head 30, the polyaxialhead 30 cannot be lifting vertically off of the bone screw 20, but itcan now rotate polyaxially about the spherical head 23 of the bone screw20. Additionally, as the spherical head 23 of the bone screw 20 passesthrough the horizontal screw head channel 32 and into the sphericalscrew head aperture 33 of the polyaxial head 30, the spherical head 23of the bone screw 20 passes and engages with the retaining tabs 35. Withthe spherical head 23 of the bone screw 20 being secured by theretaining tabs 35 within the spherical screw head aperture 33 of thepolyaxial head 30, the polyaxial head 30 is in the restrained positionor fixed position on the bone screw 20.

In a preferred embodiment, as shown by at least FIG. 12 and FIG. 14 ,the retaining tabs 35 are on the interior of the polyaxial head 30 andextend out into the horizontal screw head channel 32. The retaining tabs35 are formed in the side walls of the polyaxial head 30 to allow theretaining tabs 35 to flex outward. In the preferred embodiment, thedistance between the retaining tabs 35 is less than the diameter of thespherical head 23 of the bone screw 20. As the spherical head 23 of thebone screw 20 passes through the horizontal screw head channel 32, thespherical head 23 pushes the retaining tabs 35 outward. When thespherical head 23 of the bone screw 20 enters the spherical screw headaperture 33, the retaining tabs 35 flex back into a resting position.With the spherical head 23 of the bone screw 20 in the spherical screwhead aperture 33 and the retaining tabs 35 flexed back into the restingposition, the retaining tabs 35 thereby hold the spherical head 23 ofthe bone screw 20 within spherical screw head aperture 33 of thepolyaxial head 30. In the preferred embodiment, the retaining tabs 35alone are not intended to be a permanent retention mechanism or finalmeans of securing the polyaxial head 30 onto bone screw 20, as a surgeoncan, with nominal effort, apply sufficient force to overcome theretaining force of the retaining tabs 35 and thereby remove thepolyaxial head 30 from bone screw 20 after reversing the spherical head23 of the bone screw 20 back through horizontal screw head channel 32and into vertical screw head channel 31. However, the retaining forceprovided by the retaining tabs 35 is sufficient to prevent the polyaxialhead 30 from inadvertently disengaging from the bone screw 20 in situ,especially as the surgeon is generally position the various componentsof the overall construct.

In a preferred embodiment, as shown by at least FIG. 5 and FIG. 16 ,with the polyaxial head 30 in the retained position, the rod 40 can thenbe inserted into the rod slot 36 formed in the polyaxial head 30. In thepreferred embodiment, the rod slot 36 forms an opening that extendscephalad-caudad across the polyaxial head 30. In the preferredembodiment, the rod slot 36 also extends from the upper or proximal faceof the polyaxial screw head 30 to the spherical screw head aperture 33.This configuration, as shown by at least FIG. 9 , allows the rod 40 toseat against the spherical head 23 of the bone screw 20. Furthermore,the rod 40 sitting in the rod slots 36 prevents the spherical head 23 ofthe bone screw 20 from moving back into the horizontal screw headchannel 32, thereby preventing the polyaxial head 30 from disengagingfrom of the bone screw 20.

In a preferred embodiment, as shown by at least FIGS. 6-9 and FIG. 17 ,with the rod 40 in place within the rod slots 36 of polyaxial heads 30,the locking screw 50 can be inserted into the polyaxial head 30. In thepreferred embodiment, the locking screw 50 is formed with a drivefeature 51 configured to receive a screw driver and threads 52configured to engage with the locking threads 37 of the polyaxial head30. As the threads 52 of the locking screw 50 are threaded into thelocking threads 37 of the polyaxial head 30, the locking screw 50 forcesthe rod 40 deeper into the rod slot 36 and against the spherical head 23of the bone screw 20. This in turn forces the spherical head 23 of thebone screw 20 against the screw neck aperture 34 and the spherical screwhead aperture 33 of the polyaxial head 30, thereby preventing thespherical head 23 of the bone screw 20 from inadvertently dislodgingfrom the retaining tabs 35 holding the spherical head 23 within thespherical screw head aperture 33 of the polyaxial head 30 and slidingback through the horizontal screw head channel 32. The resulting forceimparted by the fixing of the locking screw 50 onto the polyaxial head30 locks the entire construct, preventing motion between the components.

Although the vertical screw head channel 31, rod slot 36, and lockingthreads 37 are aligned within the polyaxial head 30 in a firstembodiment, this arrangement is not meant to be limiting and otherconfigurations are possible. In a second preferred embodiment 110, asshown by at least FIGS. 18-21 , the vertical screw head channel 131, rodslot 136, and locking threads 137 are not aligned within the polyaxialhead 130 and instead at least the rod slot 136 is angled toward thespherical screw head aperture 133.

In the present disclosure, various features may be described as beingoptional, for example, through the use of the verb “may;”, or, throughthe use of any of the phrases: “in some embodiments,” “in someimplementations,” “in some designs,” “in various embodiments,” “invarious implementations,”, “in various designs,” “in an illustrativeexample,” or “for example;” or, through the use of parentheses. For thesake of brevity and legibility, the present disclosure does notexplicitly recite each and every permutation that may be obtained bychoosing from the set of optional features. However, the presentdisclosure is to be interpreted as explicitly disclosing all suchpermutations. For example, an apparatus described as having threeoptional features may be embodied in seven different ways, namely withjust one of the three possible features, with any two of the threepossible features or with all three of the three possible features.

In various embodiments elements described herein as coupled or connectedmay have an effectual relationship realizable by a direct connection orindirectly with one or more other intervening elements.

In the present disclosure, the term “any” may be understood asdesignating any number of the respective elements, i.e. as designatingone, at least one, at least two, each or all of the respective elements.Similarly, the term “any” may be understood as designating anycollection(s) of the respective elements, i.e. as designating one ormore collections of the respective elements, a collection comprisingone, at least one, at least two, each or all of the respective elements.The respective collections need not comprise the same number ofelements.

In the present disclosure, all embodiments where “comprising” is usedmay have as alternatives “consisting essentially of,” or “consisting of”In the present disclosure, any method or apparatus embodiment may bedevoid of one or more process steps or components. In the presentdisclosure, embodiments employing negative limitations are expresslydisclosed and considered a part of this disclosure.

Certain terminology and derivations thereof may be used in the presentdisclosure for convenience in reference only and will not be limiting.For example, words such as “upward,” “downward,” “left,” and “right”would refer to directions in the drawings to which reference is madeunless otherwise stated. Similarly, words such as “inward” and “outward”would refer to directions toward and away from, respectively, thegeometric center of a device or area and designated parts thereof.References in the singular tense include the plural, and vice versa,unless otherwise noted.

The term “comprises” and grammatical equivalents thereof are used hereinto mean that other components, ingredients, steps, among others, areoptionally present. For example, an embodiment “comprising” (or “whichcomprises”) components A, B and C can consist of (i.e., contain only)components A, B and C, or can contain not only components A, B, and Cbut also contain one or more other components.

The term “at least” followed by a number is used herein to denote thestart of a range beginning with that number (which may be a range havingan upper limit or no upper limit, depending on the variable beingdefined). For example, “at least 1” means 1 or more than 1. The term “atmost” followed by a number (which may be a range having 1 or 0 as itslower limit, or a range having no lower limit, depending upon thevariable being defined). For example, “at most 4” means 4 or less than4, and “at most 40%” means 40% or less than 40%. When, in thisspecification, a range is given as “(a first number) to (a secondnumber)” or “(a first number)— (a second number),” this means a rangewhose limit is the second number. For example, 25 to 100 mm means arange whose lower limit is 25 mm and upper limit is 100 mm.

Many suitable methods and corresponding materials to make each of theindividual parts of embodiment apparatus are known in the art. Accordingto an embodiment of the present invention, one or more of the parts maybe formed by machining, 3D printing (also known as “additive”manufacturing), CNC machined parts (also known as “subtractive”manufacturing), and injection molding, as will be apparent to a personof ordinary skill in the art. Metals, wood, thermoplastic andthermosetting polymers, resins and elastomers as may be describedherein-above may be used. Many suitable materials are known andavailable and can be selected and mixed depending on desired strengthand flexibility, preferred manufacturing method and particular use, aswill be apparent to a person of ordinary skill in the art.

While various embodiments of the present invention have been disclosedand described in detail herein, it will be apparent to those skilled inthe art that various changes may be made to the configuration, operationand form of the invention without departing from the spirit and scopethereof. In particular, it is noted that the respective features ofembodiments of the invention, even those disclosed solely in combinationwith other features of embodiments of the invention, may be combined inany configuration excepting those readily apparent to the person skilledin the art as nonsensical. Likewise, use of the singular and plural issolely for the sake of illustration and is not to be interpreted aslimiting.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made. For example,advantageous results may be achieved if the steps of the disclosedtechniques were performed in a different sequence, or if components ofthe disclosed systems were combined in a different manner, or if thecomponents were supplemented with other components. Accordingly, otherimplementations are contemplated within the scope of the followingclaims.

1. A polyaxial head comprising: a vertical screw head channel formedwithin a first lateral side of the polyaxial head; a screw head apertureformed within a second lateral side of the polyaxial head; a horizontalscrew head channel connecting the vertical screw head channel and thescrew head aperture, the horizontal screw head channel being defined bya first side wall and a second side wall; and a pair of retaining tabscomprising a first retaining tab formed in the first side wall and asecond retaining tab formed in the second side wall, wherein the pair ofretaining tabs are configured to flex outward to limit movement of abone screw between a first position where the bone screw is in thehorizontal screw head channel and a second position where the bone screwis reversibly secured by the pair of retaining tabs within the screwhead aperture.
 2. The polyaxial head of claim 1, wherein the firstretaining tab and the second retaining tab are aligned across thehorizontal screw head channel.
 3. The polyaxial head of claim 1, whereinthe retaining tabs extend into the horizontal screw head channel whenthe retaining tabs are in a resting position.
 4. The polyaxial head ofclaim 1, wherein the retaining tabs are separated by a distance that isless than a width of the horizontal screw head channel when theretaining tabs are in a resting position.
 5. The polyaxial head of claim1, wherein the bone screw is slidably retained within the horizontalscrew head channel when the bone screw is in the first position.
 6. Thepolyaxial head of claim 1, further comprising a screw neck apertureformed in a bottom face of the polyaxial head, wherein the screw neckaperture terminates at, and is formed continuously with, a bone screwopening formed at the first lateral side of the polyaxial head.
 7. Thepolyaxial head of claim 1, further comprising a rod slot forming aU-shaped channel that is aligned with the vertical screw head channel,wherein the rod slot is configured to receive a fusion rod and guide thefusion rod into a position abutting a bone screw retained within thescrew head aperture.
 8. The polyaxial head of claim 7, wherein theU-shaped channel defining the rod slot comprises a first channel wall atthe first lateral side of the polyaxial head and a second channel wallopposite the first channel wall.
 9. The pedicle implant assembly ofclaim 8, wherein the first channel wall is formed with a first threadedtop portion that is discrete from and opposes a second threaded topportion formed on the second channel wall, the first and second threadedtop portions being separated by a width of the U-shaped channel.
 10. Apolyaxial head comprising: a vertical screw head channel formed within afirst lateral side of the polyaxial head; a screw head aperture formedwithin a second lateral side of the polyaxial head; a horizontal screwhead channel defined by a pair of opposing exterior side walls thatconnect between the vertical screw head channel and the screw headaperture; and a pair of retaining tabs formed in the opposing exteriorside walls, wherein the pair of retaining tabs are aligned across thehorizontal screw head channel and extend into the horizontal screw headchannel when the retaining tabs are in a resting position.
 11. Thepolyaxial head of claim 10, further comprising a rod slot formed withinthe first lateral side of the polyaxial head, wherein a lateral sidewallof the rod slot is formed continuously with a lateral sidewall of thevertical screw head channel and a medial sidewall of the rod slotterminates at the screw head aperture.
 12. The polyaxial head of claim10, wherein the polyaxial head is formed from a single block of materialto provide a one-piece construction.
 13. A polyaxial head comprising: avertical channel opening formed in a bottom face of a first lateral sideof the polyaxial head; a screw head aperture formed in a second lateralside of the polyaxial head, a horizontal screw head channel formedcontinuously with, and extending away from, the screw head aperturetoward the vertical channel opening, and a rod slot forming a U-shapedchannel that is configured to receive a fusion rod, the U-shaped channelcomprising a first channel wall at the first lateral side of thepolyaxial head and a second channel wall opposite the first channelwall, wherein the first channel wall is formed with a first threaded topportion that is discrete from and opposes a second threaded top portionformed on the second channel wall, the first and second threaded topportions being separated by a width of the U-shaped channel.
 14. Thepolyaxial head of claim 13, further comprising a pair of retaining tabs,wherein the pair of retaining tabs are formed in a wall connecting thehorizontal screw head channel and the screw head aperture.
 15. Thepolyaxial head of claim 14, wherein the pair of retaining tabs flexoutward from the wall relative to the horizontal screw head channel andthe screw head aperture.
 16. The polyaxial head of claim 14, wherein thepair of retaining tabs are aligned across the horizontal screw headchannel.
 17. The polyaxial head of claim 14, wherein the retaining tabsextend into the horizontal screw head channel when the retaining tabsare in a resting position.